Document FR—2 736 190 describes a spacer grid of the above-specified type. The peripheral belt is made up of plane outer plates that are assembled to one another. The guide fins are folded relative to the planes of their respective plates towards the inside of the grid. Such a grid makes it possible to reduce the lateral deformation of the assembly that includes it. Inclining the fins inwards serves in particular to limit any risk of the spacer grids of two adjacent assemblies catching while the assemblies are being handled.
Nevertheless, a risk still exists of grids catching in certain configurations that are particularly penalizing. This applies in particular when two adjacent assemblies are offset by half the pitch of the array of fuel rods. During a handling operation, the free ends of the guide fins of one grid in a first one of the adjacent assemblies can then become engaged between two adjacent fins of a grid in the second of the two adjacent assemblies, thus catching the edge of the grid of the second assembly. If in addition, one of the two assemblies bears laterally against the other of the two adjacent assemblies to such an extent as to cause the peripheral rods of at least one of the two assemblies to bend and/or be displaced laterally, the risk of the grids of the two adjacent assemblies catching is increased. Such catching can lead to adjacent assemblies being deformed and ought therefore to be avoided.